Polishing slurry for and method of texturing

ABSTRACT

Polishing slurry for texturing the surface of a magnetic hard disk substrate has abrading particles with diameters in the range of 1-10 nm dispersed in a dispersant such as water and a water-based aqueous solution. The abrading particles may be monocrystalline diamond particles, polycrystalline diamond particles or cluster particles with monocrystalline and polycrystalline diamond particles. A method of texturing a surface of a magnetic hard disk substrate includes the steps of rotating the magnetic hard disk substrate, supplying polishing slurry of this invention on the surface of the substrate, and pressing a polishing tape on the substrate surface and running the polishing tape.

BACKGROUND OF THE INVENTION

[0001] This invention relates to polishing slurry for and a method oftexturing the surface of a magnetic hard disk substrate.

[0002] With the increase in the memory capacity of magnetic hard disksin recent years, it is becoming required to reduce the floating distanceof a magnetic head from the surface of the magnetic hard disk to lessthan 50 nm. In connection with this requirement to reduce the floatingdistance of a magnetic head, it is also becoming necessary to increasethe density of texturing marks formed on the surface of magnetic harddisk substrates to greater than 80 lines/μm.

[0003] In order to reduce the floating distance of a magnetic head, itis generally necessary to prevent both adsorption and collision of themagnetic head to and with the surface of the magnetic hard disk.

[0004] In order to prevent the adsorption of a magnetic head, thesurface of the magnetic hard disk must have a certain degree ofroughness. For this reason, a so-called texturing process is carried outon the surface of magnetic hard disks to form approximately concentriccircular indentations and protrusions referred to as texturing marks soas to thereby provide an appropriate degree of surface roughness, aswell as to improve the magnetic characteristics by providing a magneticdirectionality in the circumferential direction of the surface of themagnetic disk. In order to thus improve the magnetic characteristics, itis necessary to form very fine texturing marks and this means that thepitch of the texturing marks must be made very small or that thetexturing marks must be formed at a very high density. For the purposeof preventing collision of a magnetic head, it is necessary that therebe no abnormal protrusions on the textured surface of the magnetic harddisks.

[0005] In general, aluminum substrates having an alumite processing or anon-magnetic plating process such as Ni-P plating carried out on thesurface or glass substrates are widely used as a magnetic hard disk.

[0006] A magnetic hard disk substrate is mirror-polished and thereaftersubjected to a texturing process for forming texturing marks on thesurface. A magnetic hard disk is produced by forming a magnetic layerand a protective layer sequentially on the surface of this magnetic harddisk substrate by a known film-forming technology such as sputtering.Concentric circular protrusions and indentations are formed on thesurface of this magnetic hard disk approximately similarly to thetexturing marks formed on the surface of the magnetic hard disksubstrate.

[0007] Since these protrusions and indentations formed on the surface ofthe magnetic hard disk are the results of the magnetic layer and theprotective layer formed on top of the protrusions and indentations onthe surface of the magnetic hard disk substrate, they are higher andsloped somewhat more gently than those formed on the surface of themagnetic hard disk substrate. Thus, very fine texturing marks must beformed accurately on the surface of a magnetic hard disk substratewithout any abnormal protrusions.

[0008] It should be clear from the above explanation that the process oftexturing is a very important step in the production of magnetic harddisks (as magnetic memory media) installed in a magnetic recordingdevice or the like which is an external memory device of a computer.Indeed, it is important enough to control the recording density and thereliability of magnetic hard disks.

[0009] Such a texturing process is carried out by supplying polishingslurry on the surface of a rotating magnetic hard disk and pressing andrunning a polishing tape thereon. Approximately concentric circulartexturing marks are thereby mechanically formed by means of freeabrading particles. In this process, polishing slurry obtained bydispersing particles of one or more kinds of material selected fromdiamond, alumina and silica in a dispersing medium (dispersant) is used.A tape made of a material such as woven cloth, non-woven cloth, flockedfabric and foamed material is used as the polishing tape.

[0010] For forming very fine texturing marks without abnormalprotrusions accurately on the surface of a magnetic hard disk substrate,the material, diameter and shape of abrading particles to be containedin polishing slurry have been examined and diamond particles are nowcoming to be used widely because diamond has superior propertiesregarding resistance against wear, heat, oxidation and chemicals.

[0011] There are two kinds of diamond particles, that is,monocrystalline diamond particles and polycrystalline diamond particles.Monocrystalline diamond particles are polygonal particles with cornersaround them while polycrystalline diamond particles are roundedparticles with no corners around them. Fine texturing marks can beformed on the surface of a magnetic hard disk substrate by a texturingprocess using such monocrystalline and polycrystalline diamond particlesbut since scratches and abnormal protrusions tend to result ifmonocrystalline diamond particles are used, polycrystalline diamondparticles are now being used as diamond particles.

[0012] As shown in Japanese Patent Publication Tokkai 6-150304 (inparagraphs 0007, 0008, 0017 and 0018), for example, conventionaltexturing processes using abrading particles comprising diamondparticles are comprised of two stages. The texturing process of thefirst stage is carried out by using a polishing tape having affixedthereon abrading particles with relatively strong grinding power. In thesubsequent second stage, abnormal protrusions formed on the surface ofthe magnetic hard disk substrate in the first stage are removed by afree particle polishing method by using polishing slurry havingdispersed therein abrading particles comprising polycrystalline diamondparticles with average diameter less than 1 μm. Since polycrystallinediamond particles are round particles with no corners around them, asexplained above, having a relatively low grinding power, they can beused conveniently for the purpose of removing abnormal protrusionsformed in the first stage. In other words, texturing marks withoutabnormal protrusions can be formed as a synergistic effect of the firstand second stages of texturing process.

[0013] This prior art technology is disadvantageous in that two stagesare required and that texturing takes time and is costly. Moreover, thesecond stage is only for removing abnormal protrusions and, since thedensity of the texturing marks depends only on the first stage, finetexturing marks at recently required high densities (such as 80 lines/μmor higher) cannot be formed.

[0014] Japanese Patent Publication Tokkai 11-138424 (in paragraphs0014-0016) discloses another texturing technology by means of abradingparticles comprising polycrystalline diamond particles wherein use ismade of slurry obtained by dispersing polycrystalline diamond particlesin the form of primary particles within a liquid dispersant. This isbecause it was believed that the diameters of abrading particles wouldbecome irregular if secondary particles (coagulating particles) arepresent in the polishing slurry, causing scratches and abnormalprotrusions to be formed on the surface of the magnetic hard disksubstrate and preventing uniform texturing marks from being formed. Withsuch polishing slurry using polycrystalline diamond particles in theform of primary particles as abrading particles, however, texturingmarks cannot be formed at densities of 80 lines/μm or higher.

[0015] It is generally known that abrading particles with even smallerdiameters must be used for forming finer texturing marks and also thatabrading particles with uniform diameters must be used in order to formuniform texturing marks. If only the diameters of abrading particleswere made smaller in the aforementioned prior art technology as apolishing tape made of woven or non-woven cloth or flocked fabric isused as a polishing tape in a texturing process, the abrading particleswould easily pass through the fibers constituting such a polishing tape.If a tape made of a foamed material is used as a polishing tape, suchabrading particles would be captured easily inside indentations formedby bubbles on the surface of the polishing tape and would not actuniformly over the surface of the magnetic hard disk substrate. As aresult, their grinding force is adversely affected either locally orentirely over the surface of the magnetic hard disk substrate and asurface with uneven roughness would result. In other words, finetexturing marks cannot be formed uniformly and accurately.

[0016] Japanese Patent Publication Tokkai 2002-30275 (in paragraphs0012-0017) discloses another texturing technology using polycrystallinediamond particles as abrading particles wherein use is made of slurryobtained by dispersing in a dispersing medium coagulated polycrystallinediamond particles in the form of secondary particles produced bypositively causing polycrystalline diamond particles with diameter ofprimary particles less than 20 nm. In this technology, the primaryparticles are caused to coagulate such that apparent diameters ofindividual abrading particles (secondary particles) become larger (say,0.05-0.5 μm) and hence the aforementioned problems of the other priorart texturing technologies (such as the abrading particles easily movingthrough the fibers of a polishing tape) may be overcome.

[0017] Moreover, since the plurality of very small primary particleswhich are around the abrading particles (secondary particles) act on thesurface of the magnetic hard disk substrate, fine texturing marks can bethereby formed on the surface of the magnetic hard disk substrate. Thesecondary particles, which are relatively larger, are broken up by thepressure with which the polishing tape is pressed such that thegeneration of scratches and abnormal protrusions on the surface of themagnetic hard disk substrate can be inhibited.

[0018] If use is made of slurry having coagulated polycrystallinediamond particles (secondary particles) comprising coagulatedpolycrystalline diamond particles with primary particles havingdiameters less than 10 nm dispersed in a dispersing medium, the valleyportions of the texturing marks become too shallow and there arises theproblem that fine texturing marks cannot be accurately created.

SUMMARY OF THE INVENTION

[0019] It is therefore an object of this invention in view of theproblems of prior art technologies to provide new polishing slurry forand a method of forming very fine texturing marks on the surface of amagnetic hard disk substrate at a density greater than 80 marks/μm inthe direction of the radius without abnormal protrusions.

[0020] This invention relates to polishing slurry for and a method oftexturing the surface of a magnetic hard disk substrate. Polishingslurry according to this invention is characterized not only ascomprising abrading particles and a dispersant therefor which may bewater or a water-based aqueous solution but also wherein monocrystallinediamond particles, polycrystalline diamond particles or clusterparticles comprising monocrystalline and polycrystalline diamondparticles with diameters in the range of 1-10 nm are used as theabrading particles. Coagulated cluster particles that are coagulatedparticles of these cluster particles may also be further included. Suchabrading particles are contained in an amount of 0.01 weight % or more,preferably in the range of 0.01-3 weight % and even more preferably inthe range of 0.01-1 weight % with respect to the total of the polishingslurry. The water-based aqueous solution is an aqueous solution havingan additive added to water. The additive to be added according to thisinvention may be one or more selected from non-ionic surfactants,organic phosphoric acid esters, higher fatty acid amides, glycolcompounds, higher fatty acid salts and anionic surfactants. The contentof the additive in the polishing slurry is to be in an amount of 1-10weight % with respect to the total of the polishing slurry.

[0021] A texturing method of this invention may be characterized ascomprising the steps of rotating a magnetic hard disk substrate,supplying polishing slurry of this invention on a surface of themagnetic hard disk substrate and pressing a polishing tape on thesurface and running the polishing tape. The polishing tape may be ofwoven cloth, unwoven cloth, flocked cloth, raised cloth or a foamedmaterial. Of these materials for the polishing tape, woven cloth,unwoven cloth and raised cloth may comprise polyester and/or nylonmicrofibers of thickness in the range of 0.1-5 μm. Only the plantedpiles of the flocked cloth and the raised portion of the raised cloth,that is, only the portion of flocked and raised cloths that contacts thesurface of the magnetic hard disk being polished may comprisemicrofibers of thickness within the range given above. As for tapes of afoamed material, there are many indentations formed by air bubbles andtheir diameters are in the range of 0.1-5 μm.

[0022] According to the present invention, cluster particles andcoagulated cluster particles contained in the polishing slurry embodyingthis invention supplied to the surface of a magnetic hard disk substrateare decomposed to an appropriate degree by the pressure applied by thepolishing tape such that deep scratches and abnormal protrusions are notformed. Since such decomposed particles act on the surface of themagnetic hard disk substrate, fine texturing marks can be formed on thesurface of the magnetic hard disk. Since such decomposed particles havesharper edges than coagulated polycrystalline diamond particles, finertexturing marks can be formed than by means of coagulatedpolycrystalline diamond particle.

[0023] The present invention is applicable to the texturing of thesurface of any prior art magnetic hard disk substrate including aluminumsubstrates produced by mirror-polishing the surface of a disk of analuminum alloy and thereafter forming an electroless plating layer ofNi—P thereon or glass substrates. The present invention is particularlyadapted to the forming of fine texturing marks on a disk of a very hardand very rigid material such as a glass substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows an example of polishing device which can be used forcarrying out a texturing process according to this invention.

[0025]FIG. 2 is a photograph of a computer-generated image of thesurface of a glass substrate after a texturing process according to thisinvention.

[0026]FIG. 3 is a photograph of a computer-generated image of thesurface of a glass 10 substrate after a texturing process of ComparisonExample 1.

[0027]FIG. 4 is a photograph of a computer-generated image of thesurface of a glass substrate after a texturing process of ComparisonExample 2.

[0028]FIG. 5A is a plan view (enlarged 50 times) of the surface of awoven cloth comprising microfibers and FIG. 5B is an enlarged (by 1000times) view of microfibers constituting the woven cloth of FIG. 5A.

[0029]FIG. 6A is a plan view (enlarged 50 times) of the surface of anunwoven cloth comprising microfibers and FIG. 6B is an enlarged (by 1000times) view of microfibers constituting the unwoven cloth of FIG. 6A.

[0030]FIG. 7A is a plan view (enlarged 50 times) of the surface of araised cloth comprising microfibers and FIG. 7B is an enlarged (by 2000times) view of microfibers constituting the raised cloth of FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Polishing slurry according to this invention is characterized ascomprising abrading particles and a dispersion medium (“dispersant”)which disperses these abrading particles. Monocrystalline diamondparticles, polycrystalline diamond particles or cluster particlescomposed of these monocrystalline and polycrystalline diamond particleswith diameters within the range of 1-10 nm are used as the abradingparticles. The abrading particles need not entirely be clusterparticles. So-called coagulated cluster particles formed by clusterparticles coagulating within a dispersant may be used as abradingparticles together with cluster particles. According to this invention,cluster particles and coagulated particles within polishing slurry ofthis invention are decomposed to an appropriate degree as the slurry issupplied onto the surface of a magnetic hard disk substrate and pressedby a polishing tape and such decomposed particles also act on thesurface of the magnetic hard disk substrate together with the clusterparticles and coagulated cluster particles.

[0032] For texturing the surface of a glass substrate made of anunreinforced, reinforced or crystallized glass material, it is desirableto use cluster particles composed of monocrystalline diamond particles.It is because the surface of a glass substrate is hard and hencepolygonal monocrystalline diamond particles with many corners, ratherthan rounded polycrystalline diamond particles, can exhibit a highergrinder power.

[0033] Cluster particles may be obtained by the explosion-synthesismethod known for the production of diamond particles (such as disclosedin Japanese Patent Publication Tokkai 2000-136376) whereby a startingmaterial comprising a metallic catalyst (Co, Ni, Fe, etc.) and graphitepowder is impulse-compressed at a high temperature by the explosion ofan explosive. Those containing a relatively small amount of graphite notreacted are preferred. Cluster particles thus obtained are tasseledassemblies of very small crystalline particles with no directionality.

[0034] The diameters of the monocrystalline and polycrystalline diamondparticles are within the range of 1-100 nm because if monocrystallineand polycrystalline diamond particles with diameters in excess of 10 nmare used, more scratches and protrusion are generated and ifmonocrystalline and polycrystalline diamond particles with diametersless than 1 nm are used, the work efficiency is adversely affected.

[0035] The content of abrading particles should be 0.01 weight % withrespect to the total amount of the polishing slurry. It is preferably inthe range of 0.01-3 weight % and more preferably in the range of 0.01-1weight %. If the content of the abrading particles is less than 0.01weight %, it is difficult to form texturing marks accurately and at ahigh density on the surface of a magnetic hard disk substrate. If thecontent of the abrading particles exceeds 3 weight %, there is no changein the density or shape of the texturing marks formed on the surface ofa magnetic hard disk substrate. In other words, texturing marks can beformed on the surface of a magnetic hard disk substrate at a densitygreater than 80 lines/μm in the radial direction already with thecontent of the abrading particles less than 3 weight % (say, 1 weight %)and hence it is economically advantageous to keep the content of theabrading particles below 3 weight % to reduce the material cost.

[0036] Water or a water-based aqueous solution is used as thedispersant. Such a water-based aqueous solution is produced by adding towater a water-soluble additive with a good washing capability that canimprove dispersion of cluster particles and coagulated cluster particlesin the polishing slurry of this invention and also the lubricity duringthe texturing process. Examples of such water-based aqueous solutioninclude solutions obtained by adding to water one or more additives suchas non-ionic surfactants, organic esters of phosphoric acid, higherfatty acid amides, glycol compounds, higher fatty acid salts and anionicsurfactants. The content of such an additive (or additives) is withinthe range of 1-10 weight % with respect to the entire amount of thepolishing slurry.

[0037] Examples of non-ionic surfactant to be used as an additiveinclude the higher alcohol type, the twin type, the pluronic type andthe sorbitan type. Examples of organic esters of phosphoric acid includethe aromatic salt type, the aliphatic salt type and the aliphatic acidtype. Examples of higher fatty acid amide include lauric acid diethanolamide, ersinic acid diethanol amide, ricinoric acid isodipropanol amideand stearic acid diethanol amide. Examples of glycol compounds includealkylene glycols, polyethylene glycols and polypropylene glycols.Examples of higher fatty acid salt include potassium ricinoleate andpotassium oleate. Examples of anionic surfactant include alkyl benzenesulfonic acid, sodium dodecil sulfate and sodium stearate. Additives ofappropriate kinds should be selected, depending upon the kind and thesurface condition of the magnetic hard disk substrate to be processed.

[0038]FIG. 1 shows an example of polishing device 10 capable of carryingout a texturing method of this invention (such as disclosed in JapanesePatent Publications Tokkai 11-908010 and 11-161946. Although it is apolishing device of the type adapted to carry out a texturing process onboth surfaces of a magnetic hard disk substrate 17 at the same time, apolishing device of another kind (such as disclosed in Japanese PatentPublication Tokkai 6-195701) for texturing only one surface at a time.

[0039] For carrying out a texturing process according to this invention,the magnetic hard disk substrate 17 is set to a shaft 14 connected to adriver motor 13 and thereafter the driver motor 13 is switched on torotate the magnetic hard disk substrate 17. Polishing slurry of thisinvention is supplied onto both surfaces of the magnetic hard disksubstrate 17 through nozzles 15 and polishing tapes 12 are pressedthrough contact rollers 11 onto the surfaces of the magnetic hard disksubstrate 17 while the polishing tapes 12 are caused to run. After thetexturing process, a cleaning liquid such as water is projected onto thesurfaces of the magnetic hard disk substrate 17 through nozzles 16 toclean the magnetic hard disk substrate 17 while the magnetic hard disksubstrate 17 is kept rotating.

[0040] Examples of the polishing tape include woven cloth tapes, unwovencloth tapes, flocked fabric tapes and tapes comprising a foamedmaterial. The woven cloth, unwoven cloth and raised cloth are comprisedof fibers with thickness in the range of 0.1-5 μm, referred to asmicrofibers. Views of the surface of a woven cloth (enlarged 50 times)and that of the microfibers constituting this-woven cloth (enlarged 1000times) are respectively shown in FIGS. 5A and 5B. Views of the surfaceof an unwoven cloth (enlarged 50 times) and that of the microfibersconstituting this unwoven cloth (enlarged 1000 times) are respectivelyshown in FIGS. 6A and 6B. Views of the surface of a raised cloth(enlarged 50 times) and that of the microfibers constituting this raisedcloth (enlarged 2000 times) are respectively shown in FIGS. 7A and 7B.

[0041] Examples of flocked fabric that may be used include thoseobtained by attaching hairs known as piles onto the surface of a wovencloth, an unwoven cloth or a plastic sheet by a known electrostatic hairplanting process, as well as those obtained by sewing piles and tufts(fibers made into loops or tassels) onto a woven or unwoven cloth. Wovenand unwoven cloths which serve as the base for such flocked fabric neednot comprise microfibers as long as the piles or the tufts themselves ofthe flocked fabric are microfibers of the thickness described above.Aforementioned raised cloth is obtained by cutting a portion of thefibers constituting the surface fiber system of a woven cloth comprisingmicrofibers and raising these fibers. Only the raised portions maycomprise microfibers. The raised cloth may be one wherein either thewarps or wefts of the fiber structure of a woven cloth are microfiberswhich are cut and raised.

[0042] Thus, at least a surface portion (that is, the portion that comesto directly contact the surface of a magnetic hard disk substrate duringa polishing process) of a tape made of such a woven, unwoven, flocked orraised cloth is formed with microfibers with thickness in the range of0.1-5 μm. This is for the purpose of allowing the abrading particles tobe appropriately held on the surface portion of the tape coming intocontact with the surface of a magnetic hard disk substrate such thatfine texturing marks can be formed at a high density on the surface ofthe magnetic hard disk substrate. If the thickness of the contactingfibers of the tape is less than 0.1 μm, the points of contact betweenthe fibers at the surface portions of the tape and the abradingparticles become too few and the abrading particles cannot actsufficiently on the surface of the magnetic hard disk substrate. Thisaffects the grinding power adversely and texturing marks cannot beformed clearly and accurately. If the thickness of these fibers isgreater than 5 μm, on the other hand, the step differences betweenfibers constituting the tape surface become too large and fine texturingmarks cannot be formed uniformly on the surface of the magnetic harddisk substrate.

[0043] Tapes made of a foamed material have voids scattered throughouttherein that are formed by bubbles generated when the foamed materialwas obtained. Indentations due to such voids are scattered over thesurface of a tape made of such a foamed material. The diameters of thesesurface indentations are in the range of 0.1-5 μm.

[0044] The invention is described next by way of test and comparisonexamples.

[0045] Test Example

[0046] A polishing device as shown in FIG. 1 was used to carry out atexturing process on the surfaces of a glass substrate for a magnetichard disk.

[0047] Polishing slurry with composition as shown in Table 1 was used, Ahigh-concentration stock solution was preliminarily prepared and thepolishing slurry as shown in Table 1 was obtained by diluting this stocksolution with pure water. This was because it is a common practice tomake such a high-concentration (say, 10 times or 100 times) stocksolution available to the user such that the user has only to dilute itwith water for actual use. Cluster particles comprising monocrystallinediamond particles with diameters within the range of 1-10 nm produced byan explosion-synthesis method were used. As an additive to thedispersant for these cluster particles, a surfactant of glycol compound(alkylene glycol) was used. TABLE 1 Cluster particles 0.05 weight %Additive (surfactant of glycol compound) 5 weight % Pure water 94.95weight %

[0048] A tape of a woven cloth of thickness 700 μm comprising nylonfibers of thickness about 2 μm was used as the polishing tape.

[0049] The texturing process on the surfaces of the glass substrate wascarried out under the conditions shown in Table 2 below. TABLE 2 Rotaryspeed of glass substrate 400 rpm Running speed of tape 6 cm/minuteSupply rate of polishing slurry 15 cc/minute Hardness of contact rollers60 duro Oscillation (amplitude) 5 Hz (1 mm) Pressure by contact rollers4.5 kg

[0050] Comparison Tests

[0051] Results of aforementioned Test Example were compared with thoseof Comparison Examples 1 and 2 described below regarding the averagesurface roughness (Ra) and maximum height (Rmax) of the glass substrateafter the texturing process and the line density of texturing marks onthe surface of the glass substrate.

[0052] The average surface roughness (Ra) and maximum height (Rmax) ofthe glass substrate after the texturing process were measured by using ascan-type probe microscope (Nanoscope Dimension 3100 Series, produced byDigital Instrument Co.) and the line densities of texturing marks on thesurfaces of glass substrates were measured from the photographs ofcomputer-generated images after the texturing processes. Thesecomputer-generated images are each obtained by scanning 512 points overan arbitrarily selected area of 1.0 μm×1.0 μm on the surface of a glasssubstrate and presenting the result three-dimensionally. FIGS. 2, 3 and4 respectively show results of Test Example, Comparison Example 1 andComparison Example 2.

COMPARISON EXAMPLE 1

[0053] Polishing slurry with composition as shown in Table 3 was used tocarry out a texturing process on the surfaces of a glass substrate byusing the same polishing device and polishing tape as used in TestExample under the conditions shown in Table 2. Coagulatedpolycrystalline diamond particles used as the abrading particles of thepolishing slurry for Comparison Example 1 were polycrystalline diamondparticles (primary particles) of average diameter 20 nm coagulatedinside the dispersant. The same surfactant of glycol compound used inTest Example was also used as an additive. TABLE 3 (Composition ofpolishing slurry for Comparison Example 1) Coagulated polycrystallinediamond particles 0.05 weight % (average diameter of primary particles =20 nm) Additive (surfactant of glycol compound) 5 weight % Pure water94.95 weight %

COMPARISON EXAMPLE 2

[0054] Polishing slurry with composition as shown in Table 4 was used tocarry out a texturing process on the surfaces of a glass substrate byusing the same polishing device and polishing tape as used in TestExample under the conditions shown in Table 2. Coagulatedpolycrystalline diamond particles used as the abrading particles of thepolishing slurry for Comparison Example 2 were polycrystalline diamondparticles (primary particles) of average diameter 8 μm (about the samediameter as the monocrystalline diamond particles constituting thecluster particles of Test Example) coagulated inside the dispersant. Thesame surfactant of glycol compound used in Test Example was also used asan additive. TABLE 4 (Composition of polishing slurry for ComparisonExample 2) Coagulated polycrystalline diamond particles 0.05 weight %(average diameter of primary particles = 8 nm) Additive (surfactant ofglycol compound) 5 weight % Pure water 94.95 weight %

[0055] Results of Tests

[0056] Results of tests made on aforementioned Test and ComparisonExamples are summarized in Table 5 below. TABLE 5 Ra (Å) Rmax (Å) Linedensity (lines/μm) Test Example 1.8 25 85 Comparison Example 1 4.0 65 55Comparison Example 2 1.0 15 Lines not clear

[0057] It should be clear from FIG. 5 that Test Example has smalleraverage surface roughness (Ra) and maximum protrusion height (Rmax) andmore than 1.5 times as large line density of texturing marks thanComparison Example 1 and this means that more accurate texturing markscan be formed uniformly at a higher line density on a glass substrate ifa method of this invention is used. Comparison Example 2 shows about thesame average surface roughness and maximum protrusion height but cleartexturing marks were not formed on the surface of the glass substrateand the line density of texturing marks could not be ascertained.

[0058] In summary, the present invention has the merit that finetexturing marks can be formed uniformly on the surface of a magnetichard disk substrate without abnormal protrusions at a line density inthe radial direction of greater than 80 lines/Im.

What is claimed is:
 1. Polishing slurry for texturing a surface of amagnetic hard disk substrate, said polishing slurry comprising: abradingparticles with diameters in the range of 1-10 nm, selected from thegroup consisting of monocrystalline diamond particles, polycrystallinediamond particles and cluster particles comprising monocrystalline andpolycrystalline diamond particles; and a dispersant for said abradingparticles selected from the group consisting of water and water-basedaqueous solutions.
 2. The polishing slurry of claim 1 wherein saidabrading particles further include coagulated cluster particles insidesaid dispersant, said coagulated cluster particles being coagulatedparticles of said cluster particles.
 3. The polishing slurry of claim 1containing said abrading particles in an amount of 0.01 weight % orgreater with respect to the total of said polishing slurry.
 4. Thepolishing slurry of claim 1 containing said abrading particles in anamount of 0.01-3 weight % with respect to the total of said polishingslurry.
 5. The polishing slurry of claim 1 containing said abradingparticles in an amount of 0.01-1 weight % with respect to the total ofsaid polishing slurry.
 6. The polishing slurry of claim 2 containingsaid abrading particles in an amount of 0.01-1 weight % with respect tothe total of said polishing slurry.
 7. The polishing slurry of claim 1wherein said water-based aqueous solution is an aqueous solution havingan additive added to water, said additive being of one or more materialselected from the group consisting of non-ionic surfactants, organicphosphoric acid esters, higher fatty acid amides, glycol compounds,higher fatty acid salts, and anionic surfactants.
 8. The polishingslurry of claim 9 wherein said additive is contained in an amount of1-10 weight % with respect to the total of said polishing slurry.
 9. Amethod of texturing a surface of a magnetic hard disk substrate, saidmethod comprising the steps of: rotating said magnetic hard disksubstrate; supplying polishing slurry on said surface; and pressing apolishing tape on said surface and running said polishing tape; whereinsaid polishing slurry comprises: abrading particles with diameters inthe range of 1-10 nm, selected from the group consisting ofmonocrystalline diamond particles, polycrystalline diamond particles andcluster particles comprising monocrystalline and polycrystalline diamondparticles; and a dispersant for said abrading particles selected fromthe group consisting of water and water-based aqueous solutions.
 10. Themethod of claim 9 wherein said polishing tape is of a material selectedfrom the group consisting of woven cloth, unwoven cloth, flocked cloth,raised cloth and foamed materials.
 11. The method of claim 10 whereinsaid woven cloth, said unwoven cloth and said raised cloth comprisemicrofibers.
 12. The method of claim 10 wherein said flocked cloth hasmicrofibers that are planted and said raised cloth has microfibers thatare raised.
 13. The method of claim 11 wherein said microfibers have awidth in the 30 range of 0.1-5 μm.
 14. The method of claim 12 whereinsaid microfibers have a width in the range of 0.1-5 μm.
 15. The methodof claim 10 wherein said foamed material has a surface with indentationsformed by air bubbles, said indentations have diameters in the range of0.1-5 μm.